An enquiry has found an aerial 1080 operation that was linked to the deaths of eight cattle in the King Country substantially complied with the relevant controls and procedures.
The Department of Conservation (DOC) pest control operation was carried out over the Mapara Wildlife Reserve - 1,400 hectares of Conservation estate 35 kilometres southeast of Te Kuiti - in September 2018.
In the months before the operation, DOC staff gained permission from farmers Mark and Paula Stone to extend its operation onto 65 hectares of bush on their land.
The Stones' property borders onto the Mapara Reserve.
Three days after operation in September 2018, the Stones found eight of their cows dead.
Two months after the incident the Environmental Protection Authority (EPA) determined that it was appropriate to independently investigate the incident.
The EPA has concluded, on the balance of evidence, that livestock owned by the Stones, entered the operational area where the 1080 was dropped via an insecure fence and ate the poison.
The scope of the EPA's enquiry was to look whether the operation was compliant with Hazardous Substances and New Organisms Act controls and procedures, and determine the circumstances of the cattle's deaths.
The authority identified one breach by DOC of its standard operating procedures, where they did not advise the Stones of a decision to exclude a pocket of bush which the Stones had earlier consented to include in the operation.
However it said it was not a factor in the cattle deaths.
The report makes a set of recommendations intended to improve the consultation process for aerial 1080 operations by providing more clarity for operators and landowners.
They include the use of higher quality mapping, and better information about how 1080 behaves once spread, in terms of bioaccumulation and biodegradation.
Improvements to information, particularly for farmers, regarding "withholding periods", caution periods, as well as label and signage requirements, was also recommended.
DOC and the Stones, along with the Ministry of Health, Ministry for Primary Industries and WorkSafe, provided feedback on the enquiry report before it was finalised.